[Objective] The reinforcing effects of Sophora japonica roots on soil at different water contents and different thawing times were studied in order to provide a design basis for the soil consolidation effect of Sophora japonica in the monsoon freeze zone. [Methods] The stress-strain and strength characteristics of the root-soil composite of the Sophora japonica root system were determined using the indoor triaxial test method. The shear strength index of the Sophora japonica root-soil composite was determined under different thawing times and different moisture contents. [Results] The reinforcing effect of the Sophora japonica root system at different water contents was most obvious at low and high water contents. The reinforcing effect of the Sophora japonica root system before and after freezing and thawing was reflected in the fact that the Sophora japonica root system bound the movement between soil particles when the soil received a load, increased the occlusion between soil particles, and increased the contact surface between the roots and soil particles, thus increasing the angle of internal friction. The electron microscope scanning test showed that the Sophora japonica root system inhibited the generation and development of cracks in the soil, thus increasing the integrity of the soil. [Conclusion] The Sophora japonica root system can result in a reinforcing effect in all areas. There are different optimal root contents for different water contents. The solidification effect of the Sophora japonica root system is reflected by the increase in internal friction angle of the soil body, increasing the structural integrity of the soil.